In magnetic disc drives, reduction of the cost of manufacturing and assembly, as well as reliability of all components, is a constant goal. The spindle motor which supports one or more discs for rotation at constant speed is one of the most expensive and complex parts of the disc drive. Therefore, substantial attention is paid to steps which will make manufacturing and assembly of the spindle motor simpler, while minimizing the cost of assembly and the need for any rework.
A typical spindle motor is shown in FIG. 1, and includes a sleeve 1 supporting a hub 2 which in turn supports one or more discs 3 for constant speed rotation about a shaft 4. In this motor as well as in many other motor designs, a magnet 5 is supported axially below hub 2 on an extended portion 6 of the sleeve 1 which serves as a back iron, and immediately adjacent a stator 7. Activation of the spindle motor windings establishes a field which interacts with the magnet 5 to cause rotation of the rotor and the hub 2.
Obviously, the magnet 5 will have to be placed close to the stator 7 to optimize the interaction between these parts as well as to minimize the size of the motor. However, frequently when the sleeve and magnet are inserted into the base 8, the magnet 5 bumps into the edges of the stator laminations 9; these are metal, may have sharp edges, and could cause scratching or scaring of the soft material which forms the magnet 15. The resulting discontinuities in the magnet surface could reduce the efficiency of the motor if left alone, as well as causing magnetic particle contamination that can cause drive failure. Fixing the scars would require disassembling the sleeve 1 and shaft 4 from the base 8, and replacing the magnet structure.
Further, it can be seen that to optimize the interaction between the magnet 16 and the stator, the magnet should be properly axially aligned with the stator. This requires accurate fixturing of the magnet 5 relative to the sleeve 1 when the two are assembled.